This is usually caused by using the Global Catalog port when configuring AD into PAM. There are some differences in the information provided by the Global Catalog and standard AD ports. PAM uses the Operating System information provided by AD queries to attempt to automatically determine the proper OS & Access Methods to fill in. When a standard AD port (389 or 636) is queried it provides a full set of attributes, including the Operating System information. The Global Catalog (port 3268 or 3269) on the other hand does not provide a full set of attributes, which does NOT include the Operating System information. The main reason why the Global Catalog acts differently is because it is designed to handle multiple domains and using less attributes allows for less bandwidth and data usage when updating and querying the Global Catalog.